Create a new admin user in WordPress via code. Drop this file in the mu-plugins directory and update the variables, then load a page in WordPress to create the user. Remove the file when done.

create-admin-user.php

<?php

add_action( 'init', function () {
  
	$username = 'admin';
	$password = 'password';
	$email_address = 'webmaster@mydomain.com';

	if ( ! username_exists( $username ) ) {
		$user_id = wp_create_user( $username, $password, $email_address );
		$user = new WP_User( $user_id );
		$user->set_role( 'administrator' );
	}
	
} );

To send an email to the new user, just add this below line 12:
wp_new_user_notification($user_id, $password);

On multisite, just do this to grant super admin privileges: grant_super_admin( $user_id );

Thanks for sharing this.

I knew this would come in hand one day, again...

Would this user still show up in the regular user list for all other admins?

Would this user still show up in the regular user list for all other admins?

Yes, of course.